Herbicide Dispersal Patterns: I. As a Function of Leaf Surface

The distribution pattern of MCPA ([(4-chloro-o-tolyl)oxy] acetic acid) on leaf surfaces of three species was studied using the cathodoluminescence detection mode of a scanning electron microscope. On low-wax-content sugarbeet (Beta vulgarisL.) leaves MCPA concentrated in the depressions over the anticlinal cell walls when applied at high volumes (748 and 374 L/ha). At low volumes (23 L/ha), numerous small deposits of MCPA were randomly distributed over both anticlinal and periclinal walls. These distinct patterns were independent of herbicide concentration. Regardless of spray volumes, MCPA remaining on the waxy leaf surfaces of cabbage (Brassica oleraceaL.) coalesced into small thick deposits. Large spray drops from high application volumes shattered on impact with the stellate hairs of turkey mullein (Eremocarpus setigerusBenth.) resulting in some MCPA reaching the leaf surface. Spray drops from low application volumes did not shatter but lodged on the hairs with very little reaching the leaf surface.